Microwave frequency meter



Jan. 19, 1954 s. A. JOHNSON 2,666,904

MICROWAVE FREQUENCY METER Filed May 28, 1948 a @4 w/w cavity in front of thezpiston,

' diameter of the cylinder, and A and B are known constantsa-m, g

- from thepiston-axis.

Patented Jan. 19, 1954 es PATENT OFFICE I FREQUENCY METER j ration of; New .York

This inventior i relates to frequency meters of f waves in the is concerned with a fref thetype wherein the resonant The resonant fre-. .an arrangement where f is the frequency,

dis the internal The resonant frequency of the cavity is varied StanlyA'. Johnson, New York, 'N;"Y., assignor to ePolytechnic. Research and Development Comlpany Incorporated, Brooklyn, N. 1L, a corpo- Ap plication May 28, 1948, Serial No. 29,910 ii Claims.- (01.633 83) strained to move in paths at right angles to each other. Another feature of my invention is the provision of a vacuum tight seal for, the piston rod where it passes, through the cavity ,wall.

One embodiment of my invention is illustrated in the accompanying drawing in which:

' Figure 1 is a.sectional view of the frequency meter taken in.a vertical cutting plane passing through the axis of the cavity cylinder; and

Figure 2 .isran end elevational viewof Figure 1 with the casingjof. the meter, shown in section along thecutting plane 2v 2 of Figure 1.

Referring to; the drawing, 1| indicates an enclosed casingforthe meter and la is a removable l is the length of the top wall of the casing from which the meter elements aresuspehdedwithin the casing. A short length of rectangular waveguide 2 passe through thelcasing .l ,.asi shownr n'E eure 2 an is p oby adjusting-theiposition of the piston within the cylinder, to vary :the length 1. piston hasibeenaadjusted within the cylinder by Heretofore, the

means of a micrometer screw which produced uniform axial movement of the piston for equal angular rotation of the: screw. -While this arrangement provides great accuracy of measurement of the movement of the piston, it is not especially'suitable for the indication of the resonant -frequencw This becomes apparent from the foregoing-equation where it will be seen that the frequency "of the resonant cavity does not bear a simple relation tothe length of the cavity,

and heretofore it has been necessary to refer to.

cumbersometables or charts inorder to convert the reading-fiof-the micrometer screw into corresponding frequency readings.

An- .object ofthe present invention is to devise an arrangement for=moving the-piston of. the wave-meterso that there will be substan-. tially a linear relation between the resonant free .vi iv h co pling fla s...? amli on posite vends thereof The wave guide is supported from the top wall la by meansof a pair t ert a ar ta ,4. a tran ed a Opposite sides of the casing as shown in Figure 2 and having their upper ,ends fastened to the cover la. The waveguideZ is, positioned within slots formed in the lower ends of supports; and 4 and is held in, these slots by bridge pieces 3a and 4a. The side walls of the casing l as viewed in Figure 2 are, provided withvertical slots through which the waveguide zpasses and by whichthe waveguide may be removed from the casingjwhen the cover la is removed. Theseslots arecovered by the guide 'upporti ng pieces 3 andi l A cavity cylinder 5 is mounted above the waveguide 2 within'the casing I and communicates withthe, interior of the waveguide} through anaperture' 5a formed in a cylindrical Wall of the cylinder near the, left end as shown in Figure ,1. ,.One end ofthe cylinder 5 is closed by quency of tlhe eavi-ty. and the angular movement ofthe adjustinglscrew,

- According to the present invention, a special 1 transmission mechanism; is interposed between the adjusting screw andsthe'movable piston for translating the uniform axialmovement 'of the plied to the piston of themeter. For this purpose-,-the adjustingrscrew is arranged at right angles to -the;ax-is of 'the-piston rod and is offset The axial movement of the adjusting screwistransmittedto the piston rod through a link element interposed between the screw andthe rod and having its ends conscrew into a variable; rectilineanmovement apvso end plate 5b,,and 1the cylinder is d vided into two compartments by acenterplate 5c," and a removable endiplatejd' closes the other end. A pisn. 6 rslideab ,m' unte Within bearings providedat hc.. enter ptth .s ates? and 5d 1 and,carries','on onej end apiston [mounted witht e tesonant .QaVi Y-QA ate, damping materialgsuch aspolyiro s: positioned behind the piston 1, to prevent'lo of; wave ener'gy around the edgeofthe'piston; The plates 51) and 5c are hermetically sealed tqthe cylinder 5 and the, resonant c'avityflenclosed between formed of these plates maybe exhaustedjth rough exhaust .,tube is and may 09 sealed in evacuated condition or other 'ili'sef maintair' ed under vacuum pressure Thebe'aring for the'pistonrod t in the plate 50 is hermetically sealed by means of a bellows 9 having one end sealed to the plate 50 and the other end sealed to a bellows head 9a carried by the piston rod 6 and being sealed thereto. A compression spring in is interposed betweenthe plate 50 and a stop plate lBa removably carried by the bellows head 9a. The purpose of this spring is to normally urge the piston 7 towards the right in Figure l,or towards the position of lowest frequency.

The outer end of piston rod 6 extends into a transmission box ll which is mounted upon the end plate Ed by any suitable means such as screws lla. The box H i provided with a removable cover plate I lb arranged at right angles to the bottom wall of the box which is parallel to the axis of the piston rod 6 as shown in Fig ure 1. A pair of brackets He and He are secured to opposite walls of the box ll and are connected to the cover plate la for the purpose of bracing the box with respect to the plate la.

A micrometer adjusting or operating screw l2 has threaded engagement with a nut element lld mounted in the top wall of the box ll and is thereby positioned with its axis parallel with the cover plate I Id of the box. The screw l2 has a stem l2a carrying a drum dial l2b positioned within a circular opening formed in the cover plate la and provided with an operating knob l 20. The stem l2a of the screw I2 is journaled within a supporting bracket formed of two vertical legs l3a and l3b secured to opposite sides of the box I l and having a horizontal bridge portion l3c in which the stem l2a is journaled.

The axial movement of the screw I2 is transmitted to the piston rod 6 by means of a link element l4 movably mounted within the box ll. This element carries a roller l la mounted with a slot formed in one end of the link and journaled upon an axle Ma carried by the link. The roller Ma bears against the inner face of the cover plate llb. A second roller l4b is mounted within a slot formed in the other end of link l4 and is journaled upon an axle l4b' carried by the link l4, and this roller bears against the inner face of the bottom wall of the box ll. An inverted U-shaped bracket I5 is mounted on the axle I la immediately below the end of the screw l2, and the axial movement of the screw is transmitted to the bracket l5 by means of a single ball bearing l6 interposed between the screw l2 and the bracket IS. A second U-shaped bracket l! is carried by the axle Nb and is adjustably connected with the end of piston rod 6 by means of screw [8 which is removably connected to the bracket IT.

The compression spring I!) constantly urges the piston rod 6 towards the right as shown in Figure 1, and this urges the link l4 upwardly to maintain contact between the bracket i5 and the ball l6 and to maintain the ball in contact with the end of the screw l2. This arrangement eliminates all play or lost motion between the screw l2 and the piston I. When the screw I2 is rotated in a direction to advance the screw into the box II, the link I4 is moved by the screw to transmit motion to the piston rod 6, and thereby move the piston 1.

Since the screw l2 makes many revolutions for operation of the piston 1 throughout its range, it is desirable to provide a counter dial in the form of a disk l9 positioned below the cover plate la and having suitable graduations formed on its upper face which may be viewed through an opening la formed in the cover plate. The

counter dial I9 is mounted upon a shaft l9a which is journaled in a sleeve l9b carried by a mounting plate 20 secured to the top wall of the box ll. The counter dial I9 is driven from the screw l2 by means of a speed reducing gear train including a main pinion 2l mounted on the stem l2a of the screw l2 and driving a gear 22 mounted upon a shaft journaled in the sleeve 23 supported on plate 20 and driving a pinion 24 which meshes with a gear 25 carried by the shaft I911. The drive pinion 2| is of considerable width to maintainv engagement with the gear 22 throughout the range of axial movement of the screw l2. It will be understood that the drum dial l2b may carry graduations on its upper face which will represent fractions of the graduations carried by the dial l9. Both graduations preferably are in terms of frequency.

Operation of the frequency meter is as follows: with the parts shown in Figure 1, the piston I is in the position of lowest frequency. When the operating screw I2 is rotated in a direction to advance into the box ll, the link l4 moves through a constantly varying angle of inclination to transmit a variable rate of movement to the piston rod 6 and thus to the piston l. Specifically, the relation between the movement of the piston rod 6 and the movement of the screw l2 is represented by a section of an ellipse. From the equation given above, it will be found that the relation between the frequency and the axial movement of the piston l is represented by a hyperbolic curve, and from the equation, it will be seen that as the length of the cavity becomes smaller, the frequency increases, and at the very low values of length, the frequency increases at a very high rate. By properly designing the transmission linkage, the elliptical variation of motion transmitted to the piston I through the link l4 slows down the rate of movement of the piston l as the length of the cavity decreases into the high frequency range and serves to compensate for the non-linear variation of the frequency with respect to the axial movement of the piston. By proper design of the transmission linkage, including the length of the piston rod, the length of the link [4 and its initial inclination, a substantially linear relation may be obtained between the resonant frequency of the cavity and the angular movement of the screw l2, so that the dials l2b and I9 may be calibrated directly in frequency, and the calibration will be substantially uniform. It will be noted that as the screw l 2 moves from the position of lowest frequency towards the position of highest frequency, the rate of movement of the piston 6 progressively decreases, and as the link l4 approaches the horizontal position, very little axial movement of the piston l is produced for a given axial movement of the screw l2. When screw l2 is moved from one position to a position of lower frequency the piston 1 is moved by the force of spring l0, and the screw l2 merely limits the amount of movement.

It is desirable to form the various parts of the meter of Invar metal to insure against changes in the calibration of the meter with changes in temperature.

It will be understood that my invention is not limited to the specfiic form disclosed herein and that various changes may be made without departing fromfthe principle of operation. For example, instead of using the arrangement described in which the nut of the adjusting screw remains stationary and the screw moves axially, the screw may be held against axial movement and the travelling nut would be connected to drive the upper end of the link I.

I claim:

1. A frequency meter of the cavity resonator type adapted to sustain electromagnetic wave oscillations and comprising a cylinder having a movable piston mounted therein, a screw for adjusting said piston, and a variable speed transmission device controlled by the axial movement of said screw for moving said piston in a progressively decreasing amount for a given extent of rotation of said screw as said transmission device moves said piston from a position of low frequency to a position of high frequency.

2. A frequency meter of the cavity resonator type adapted to sustain electromagnetic wave oscillations and comprising a cylinder having a movable piston mounted therein, a rigid link element, means mounting said link for movement so that one end moves along the axis of said piston and the other end moves along a path at right angles to said axis, an operating screw mounted with its axis parallel with said path, means controlled by the rotation of said screw for effecting movement of the said other end of said link along said path in proportion to the axial movement of said screw, and means connecting the said one end of said link to said piston to effect a corresponding movement of said piston along its axis.

3. A frequency meter of the cavity resonator type adapted to sustain electromagnetic wave oscillations and comprising a cylinder having a movable piston mounted therein, spring means normally urging said piston towards its position of lowest frequency, a rigid link element, means connecting one end of said link element to said piston and for constraining the movement of said end along the axis of said piston, means for constraining the movement of the other end of said link along a path at right angles to the axis of said piston, and a screw mounted for axial movement along said path and serving as a stop for limiting the movement of said other end of said link along said path under the action of said spring.

4. A frequency meter of the cavity resonator type adapted to sustain electromagnetic wave oscillations and comprising a cylinder having a movable piston mounted therein, a movable operating element mounted for movement along a path at right angles to the axis of said piston, and a rigid link element connected between said piston and said movable operating element for transmitting the movement of said operating element to said piston.

5. A frequency meter of the cavity resonator type adapted to sustain electromagnetic Wave oscillations and comprising a cylinder having a movable piston mounted therein, a rotary operating shaft, and a motion translating mechanism connecting said operating shaft to said piston and translating uniform rotary movement of said shaft into progressively decreasing axial movement of said piston as said piston moves in a direction to decrease the length of the cavity in said cylinder.

6. A frequency meter of the cavity resonator type adapted to sustain electromagnetic wave oscillations and comprising a cylinder closed at both ends and having a partition mounted therein for dividing said cylinder into a resonator section and a second section, a piston arranged within said resonator section and having a piston rod extending through a central bearing in said partition and through a central bearing in the end wall of said second section, a cylindrical bellows surrounding said piston rod within said second section and having one end thereof hermetically sealed to said partition, means for hermetically sealing the other end of said bellows to said piston rod adjacent the bearing in said end wall, a compression spring located within said second section and exerting a biasing force on said rod in a direction tending to increase the length of the cavity in front of said piston, a rigid link, means pi-votally connecting one end of said link to the end of the said rod, means guiding the other end of said link for movement along a path at right angles to the axis of said rod, an operating screw mounted with its axis parallel with said path and positioned so the end thereof engages the outer end of said link and limits the movement of said piston under the action of said spring.

7. A frequency meter adapted to sustain electro-magnetic wave oscillations and comprising a closed cylinder, a plunger passing through one end wall of said cylinder and being axially move- Lble within said cylinder to vary the resonant frequency of said meter, a rigid link element, means mounting said link for movement so that one end moves along the axis of said plunger and the other end moves along a path at right angles to said axis, an operating screw mounted with its axis parallel with said path, means controlled by the rotation of said screw for effecting movement of the said other end of said link along said path in proportion to the axial movement of said screw, and means connecting the said one end of said link to the outer end portion of said plunger to effect movement of said plunger along its axis.

8. A frequency meter adapted to sustain electro-magnetic wave oscillations and comprising a closed cylinder, a plunger passing through one end wall of said cylinder and being axially moveable within said cylinder to vary the resonant frequency of said meter, spring means normally urging said plunger towards its position of lowest frequency, a rigid link element, means connecting one end of said link element to the outer end portion of said plunger and for constraining the movement of said end of said link along the axis of said plunger, means for constraining the movement of the other end of said link along a path at right angles to the axis of said plunger, and a screw mounted for axial movement along said path and serving as a stop for limiting the movement of said other end of said link along said path under the action of said spring.

STANLEY A. JOHNSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 849,166 Shauan Apr. 2, 1907 1,932,498 Wilcox Oct. 31, 1933 2,106,768 'Southworth Feb. 1, 1938 2,436,640 Fredholm et a1 Feb. 24, 1948 2,466,439 Kannenberg Apr. 5, 1949 2,466,765 Hartman Apr. 12, 1949 2,475,778 Campbell July 12, 1949 2,503,256 Ginzton Apr. 11, 1950 

